In the past, the polyphenylene ether resins have used for home appliances, OA apparatuses, and automobile parts because these resins have high electrical insulation properties, and have heat resistance, hydrolysis resistance, and flame retardancy.
In such circumstances, to improve the flame retardancy (particularly dropping prevention properties during burning) of the polyphenylene ether resin composition, methods of adding a fluorine resin (such as polytetrafluoroethylene) to the resin composition are proposed (see Patent Documents 1 and 2, for example).
Moreover, the recent resin films need to have performances according to various applications such as electrical insulation properties, heat resistance, hydrolysis resistance, and flame retardancy. Utilizing excellent properties such as electrical insulation properties, heat resistance, hydrolysis resistance, and flame retardancy, the films obtained by forming the polyphenylene ether resin into a sheet have been increasingly used in wider applications (see Patent Document 3, for example).
In the recent proposals, utilizing properties such as durability (hydrolysis resistance), low-temperature shrink properties, and electrical insulation properties, the polyphenylene ether resin film is applied to the back sheet used in photovoltaics (see Patent Documents 4 and 5, for example).
Solar batteries receive attention as an alternative energy source to fossil fuels these days. The solar batteries typically have a layer structure in which a solar battery element that performs photovoltaics is interposed between a transparent glass plate and a back sheet. A sealing material is used to embed the gaps between the solar battery elements. The package of the solar battery elements into a module is called a “solar battery module.” The solar battery element has a sunlight receiving surface (front surface) covered with a transparent reinforced glass or the like, and the other surface receiving no sunlight (rear surface) covered with a back sheet.
The sealing material needs to exhibit high adhesiveness to seal the solar battery elements. For such a sealing material, ethylene vinyl acetate (hereinafter, also referred to as an “EVA”) and the like are used. The solar battery elements are sealed by filling the sealing material into the gaps between the solar battery elements and performing heat press when glass, the solar battery elements, and the back sheet are integrated by lamination. The sealing can prevent the solar battery elements from moving when the solar battery module is produced. Typically, heat at approximately 150° C. is applied in this heat press step. Accordingly, the back sheet needs to have heat resistance at a certain extent.
Further, because the solar battery module is used outdoors, the members that form the solar battery module need to have sufficient weatherability and durability. From such viewpoints, plastic materials and the like having high heat resistance and weatherability are used for the back sheet.
Examples of the conventional plastic materials used for the back sheet include polyester resins. However, it is pointed out that polyester resins have insufficient hydrolysis resistance that gives an influence on weatherability.
To solve this problem, a polyester sheet having a specific intrinsic viscosity (IV) and biaxially stretched to improve hydrolysis resistance is proposed (see Patent Document 6, for example). Further, a sheet formed of layered gas barrier transparent deposition sheets comprising polycarbonate and inorganic oxide is proposed to improve hydrolysis resistance fundamentally (see Patent Document 7, for example).